In industry, oily waste waters are produced in various processes located in the steel and aluminum industries, chemical processing industry (CPI), automotive industry, laundry industry and refinery industry. In these industries, highly refined oils, lubricants and greases contact water for various purposes according to the particular industry. This results in a highly dispersed or severe oil-in-water emulsion in the waste water streams.
For example, in the steel and aluminum industries, waste water from steel and aluminum mills using hot rolling mills contain lubricating and hydraulic pressure hydrocarbons. Waste water from cold rolling mills contains oils that lubricates the sheets and reduces rust. Specifically, in cold rolling mills, oil-in-water emulsions are sprayed on the metal during rolling to act as coolants. Also, metalworking plants generate waste water streams containing lubricating and cutting oils, lapping and deburring compounds, grinding and other specialty fluids. These oils are generally highly refined hydrocarbons.
Refinery waste oil comes from two different sources: (1) Skimmings from the water clarification equipment, i.e., DAF's, API separators, and consisting mainly of crude oil; and, (2) Leakage from processes collected via traps and drains throughout the plant. This oil is usually sent to a waste water treatment plant.
One type of waste oil is formed during the process of removing dispersed oil from waste water in waste water treatment plants. The oil (called "float" or "skimmings") is concentrated in clarification vessels such as dissolved air floatation units (DAFs), induced gas floatation units (IGFs), corrugated plate interceptors (CPIs), and holding tanks. The oil floats to the top of these units, is removed by mechanical means and then stored. This waste oil may then be disposed of by incineration, sent to oil reclamation sites, or treated on-site. These waste oils have a minimum of 50% to 95% oil and contain emulsified water and solids which are stabilized by chemicals used to remove the oil from the waste water.
Waste waters from cotton and wool manufacturing plants contain oils and greases from the scouring, desizing and finishing operations. Finishing oils used in cotton and wool manufacturing to reduce friction and snagging of fibers on spinning machines end up in the waste water. Processes in other industries also generate oily waste water such as: paints, surface coatings, and adhesives; soaps and detergents; dyes and inks; and the leather industry. In each of the industries described above, the oils used in process ultimately contaminate waste water streams as highly dispersed or oil-in-water emulsions.
The emulsified oil in the waste water is typically present in the range of several hundred to tens of thousands of ppm. It is critical to remove this oil from a waste stream before discharge from an environmental standpoint. The United States Environmental Protection Agency has placed strict restrictions on total oil and grease (TOG) limits for water that is to be discharged into public drinking water supplies or into open bodies of water. The removal of this oil is very critical to meeting the established discharge limits for total dissolved solids (TSS), carbon oxygen demand (COD), biological oxygen demand (BOD) and total organic carbon (TOC) into local sewers and rivers. Not only has the EPA established strict limits on the oil and grease discharge, these industries are affected by local city ordinances as well.
An emulsion is an intimate mixture of two liquid phases, such as oil and water, in which the liquids are mutually insoluble and where either phase may be dispersed in the other. An oily waste emulsion, in which oil is dispersed in the water phase, may contain any of a variety of oils in a wide range of concentrations. These oils are defined as substances that can be extracted from water by hexane, carbon tetrachloride, chloroform, or fluorocarbons: In addition to oils, typical contaminants of these emulsions may be solids, silt, metal particles, emulsifiers, cleaners, soaps, solvents, and other residues. The types of oils found in these emulsions will depend on the industry. They may be lubricants, cutting fluids, heavy hydrocarbons such as tars, grease, crude oils, and diesel oils, and also light hydrocarbons including gasoline, kerosene, and jet fuel. Their concentration in the waste water may vary from only a few parts per million to as much as 5 to 10% by volume.
A stable oil-in-water emulsion is a colloidal system of electrically charged oil droplets surrounded by an ionic environment. Emulsion stability is maintained by a combination of physical and chemical mechanisms.
Emulsions may be broken by chemical, electrolytic, or physical methods. The breaking of an emulsion is also called resolution, since the aim is to separate the original mixture into its parts. Chemicals are commonly used for the treatment of oily waste waters, and are also used to enhance mechanical treatment. In breaking emulsions, the stabilizing factors must be neutralized to allow the emulsified droplets to coalesce. The accumulated electric charges on the emulsified droplet are neutralized to allow the emulsified droplets to coalesce. The accumulated electric charges on the emulsified droplet are neutralized by introducing a charge opposite to that of the droplet. Chemical emulsion breakers provide this opposite charge, and are thus usually ionic in nature.
The treatment of oily waste water in normally divided into two steps, i.e., coagulation, which is the destruction of the emulsifying properties of the surface active agent or neutralization of the charged oil droplet, and flocculation, which is the agglomeration of the neutralized droplets into large, separable globules. The term oily waste water refers to an oil-in-water emulsion which may contain oil, dispersed solids, and water.
Historically, dry polymers, solution polymers, and inverse emulsion latexes have been used to treat the waste water. Each material has its own advantages and disadvantages.
Water-in-oil emulsions of water-soluble vinyl addition polymers, referred to herein as latex polymers, are used quite frequently, though they have several disadvantages. The first disadvantage is that the latex polymer must be inverted prior to use, which complicates the process of feeding the polymer into the system. Numerous problems associated with this feeding method have caused many users to avoid latex polymers. Additionally, the latexes generally have a narrow treating range, which can result in over-treatment at higher dosages. Furthermore, latex polymers add even more oil to the stream to be treated because latex polymers typically include 20-30% by weight of a hydrocarbon continuous phase. Of course, adding more oil and surfactants to the system is undesirable when treating waste water streams.
Although solution polymers require no prior make up, active polymer content and molecular weight characteristics of these polymers are inherently limited. These coagulants are often used to break oil-in-water emulsions, but they are unable to flocculate the dispersed oil, thus requiring an adjunct chemical (a flocculant) to complete the process.
Water-soluble cationic polymers for the removal of emulsified oil from oil field produced water have been disclosed in U.S. Pat. No. 5,330,650. Dispersions of water-soluble cationic polymers for the removal of emulsified oil from ethylene quench water have been described in U.S. Pat. No. 5,294,347. A method for recycling waste oil fluids with a dispersion of a water-soluble cationic polymer is disclosed in U.S. Pat. No. 5,332,507. Additionally, water-soluble dispersion polymers for purposes such as flocculating and/or dehydrating sludge or for separating and treating oil-containing industrial waste water have been disclosed in U.S. Pat. Nos. 4,929,655; 5,006,590; 5,708,071; 5,587,415; and JP 7-71678. However, such polymers are hydrophobic dispersions, as they are polymerized from at least 5% of monomers of general formula II. ##STR1##
Moreover, hydrophilic dispersion polymers have been disclosed for use in the pulp and paper industries to increase retention and drainage in EP 0 831 177 A2; for deinking in U.S. Pat. No. 5,750,034 and for treating recycled coated broke in EP 0 821 099 A1. However, there is no indication that such polymers would also be demulsifiers.
Water-soluble cationic dispersion polymers having less than 5 mole percent benzyl functionality which may be used as demulsifiers are disclosed in U.S. Pat. Nos. 5,614,602; 5,696,194 and 5,707,533. However, the dispersion polymers disclosed therein are hydrophobic, due to the incorporation of substituted acrylamides as from 1 to about 50 mole percent N-alkyl acrylamide, N,N-dialkylacrylamide or mixtures thereof. Moreover, attempts to make polymers without incorporation of substituted acrylamide monomers failed, as disclosed in comparative examples 1 and 2, column 9 of U.S. Pat. No. 5,707,533. Therefore, these patents represent a teaching away from the hydrophilic dispersion polymers of the type which we have discovered.